https://scholars.wlu.ca/etd/1780

Hickman, Jennifer L (2016) Seasonal Evolution of Active Layer Formation in Subarctic Peat Plateaux and Implications for Dissolved Organic Matter Composition and Transfer, Scholars Commons Laurier - Theses and Dissertations, https://scholars.wlu.ca/etd/1780

Peat-accumulating wetlands are ecosystems whose rate of photosynthetic production of organic matter is greater than that of its decomposition, resulting in a build up of soil organic matter that may take centuries to fully decompose. Carbon (C) stocks within these ecosystems are a function of inputs from photosynthesis, and losses from heterotrophic decomposition. Due to the short growing season and overall cold climate of boreal and tundra regions, C has been accumulating within these landscapes, mostly in soil organic matter, since the last glaciation. Climate change, predicted to result in rising temperatures and increased precipitation, has begun to degrade the underlying permafrost of peat plateaux. Hydrologically, permafrost below the active layer acts as an impermeable layer, similar to bedrock, limiting the movement and storage of groundwater to the seasonally thawed active layer. The presence of seasonal ice in the active layer reduces the hydraulic conductivity and available storage capacity, significantly reducing water infiltration, and potentially increasing the occurrence of surface ponding. Accumulated water in surface pools maintains soil moisture levels for longer periods of time, and are often the locations of the deepest thaw depth due to the downward transfer of latent heat aided by the increased thermal conductivity of the peat in the presence of water. Understanding the linkages between the hydrology, the energy balance, and chemical release into surface and groundwater is essential to predicting the response of these landscapes to future climate change. To examine how Northern peatlands are responding to recent warming, two study sites (62° 27’ N, 114° 31’ W; 62° 33’ N, 114° 00’ W) outside of Yellowknife, NT, were instrumented between October 2012-October 2013 to monitor groundwater carbon chemistry, ground thermal and moisture regimes, organic matter decomposition rates, and active layer development over an entire summer period. An integral precursor to site-wide degradation, surface microtopography has been identified as a major determinant in the future evolution of peat plateaux into permafrost-free, bog-like environments. A Biochambers laboratory peat monolith experiment replicating the climatic conditions of a hummock and a depression in the natural system revealed that during the spring freshet while the ground remains frozen, the largely ice-free hummocks function as water contributors to ice-rich depressions, acting as water catchments. This transfer of water aids in the mobilization of DOM from hummocks into depressions, where it potentially accumulates over long time periods and is susceptible to export as the peat plateaux degrade. The accumulation of water in depressions prevents complete freeze-back of the active layer in the winter, allowing microbial activity and DOC production to occur year-round. The formation of supra-permafrost taliks has also been observed as an outcome of trapped heat beneath the seasonally frozen active layer and above the permafrost table, which, over time, may form interconnected subsurface flowpathways for DOM export. As warming commences over time, it is thought that the physical and carbon chemistry characteristics of the degraded portion of the plateaux may act as a proxy for future landscape change.

https://scholars.wlu.ca/cgi/viewcontent.cgi?article=2882&context=etd